I am looking into getting some of these. I am providing the link in hopes that in might help out someone else. I would think that the people who have nice original windows and want to keep them would be esp. interested. Be sure to check out the photo Gallery. If anyone knows more about these or has seen them I would love to hear about it. http://www.windotherm.com/index.htm

Would be a good idea for me, except that most of the old double sash windows I have are in really bad shape, installed in the 1930's and not very well maintained. I've replaced some of them with Andersons.Even with the triple track storm windows the old windows are still drafty. The Andersons are great (and expensive), I installed tilt-wash ones upstairs. Still have a lot more to change, all I need is the $$$.I've been slowly replacing all the windows at my mother's house as well, it has the old metal casements.